This invention relates generally to the preparation of certain Group 4 metal amide complexes by means of an amine elimination process to produce metal complexes. More particularly the present invention relates to a novel process for conversion of initial Group 4 metal amides to the corresponding metal diamide complexes.
The manufacture of Group 4 metal amide complexes has been previously taught in U.S. Pat. No. 5,312,938, U.S. Pat. No. 5,597,935, U.S. Pat. No. 5,861,352, U.S. Pat. No. 5,880,302, U.S. Pat. No. 6,020,444, and U.S. Pat. No. 6,232,256, and elsewhere. In WO02/38628 Group 4 metal complexes containing “spectator ligands” such as amino-substituted cyclic amine compounds were prepared using such a process in the first step of a two step process. Suitable amide complexes include Group 4 metal tetra(N,N-dialkylamino) compounds, especially titanium-, zirconium- or hafnium-tetrakis(N,N-dimethylamide) compounds. Suitable alkylating agents include trialkylaluminum compounds, especially trimethylaluminum, and alumoxanes.
A persistent problem of the foregoing processes is the inability to produce the diamide complex in high yield and purity. Because the exchange step is an equilibrium process, complete conversion generally cannot be attained even after resorting to the use of elevated temperatures and/or venting or vacuum removal of amine byproducts. A process in which complexation of the metal by a ligand is facilitated, thereby resulting in the use of lower reaction temperatures, shorter reaction times, and/or characterized by higher yields, is still desired.